Measuring alternating electric currents.



No. 7I4,973. Patented Dec. 2, |902.

' v M. E. THDMPSDN.

MEASURING Al-.TERNATING ELECTRIC CURRENTS.

(Application led Dec. 30, 1896.) (No Modal.) 2 Shee'ts--Sheefl.

NU. 7|4,973. Patented D86. 2, |902.

M. E. THOMPSON. MEASUBING ALTERNATING ELECTRIC CURREIITS.A

(Application med Dec. 30, 1896.)

2 Sheets-Sheen 2.

(No Model.)

Unire lSrarns PAfrnNr OFFICE.

MILTON E. THOMPSON, OF RIDGWAY, PENNSYLVANIA, ASSIGNOR, BY MESNEASSIGNMENTS, TO THE GENERAL ELECTRIC COMPANY, OF SCHENECTADY, NEW YORK,A CORPORATION OF NEW YORK.

MEASURING ALTERNATING ELECTRIC CURRENTS.

SPECIFICATION forming part of Letters Patent No. 714,973, dated December2, 1902- Application filed December 30, 1896. Serial No. 6517.453. (Nomodel.)

To all whom t may concern,.-

Beit known that I, MILTON E. THoMPsoN,of Ridgway, in the county of Elkand State of Pennsylvania, have invented an Improvement in MeasuringAlternating Electric Currents, of which the following description, inconnection with the accompanying drawings, is a specification, likecharacters on the drawings representing like parts.

This invention relates to that class of electric meters for alternatingelectric currents in which a movable element is acted upon inductivelyby the influence of two or more alternating magnetic fields of differentphase. In meters of this class as heretofore constructed I have foundthat while such meters, if properly calibrated, will accurately registernon-inductive loads they fail to give accurate registration with loadsof high inductance, and in extreme cases I have known the meter toactually run backward with loads of this latter class. I have also foundthat eX- treme changes of periodicity are liable to affect the accuracyof meters of this type, owing to the fact that such changes affect themagnetic density in the iron core of the reactance-coil used with suchmeters, the magnetism of such iron cores not varying in proportion tothe current circulating around them.

The object of this invention is to remedy the defects above referred toand to provide an electric meter which will measure the electric energyin the work-circuit whether that energy be consumed by devices havingiuductance or not-as, for example, the energy consumed by electricmotors and inductance-coils as well as incandescent lamps.

In the case of the electric motors, inductance-coils, or other inductiveloads the electric energy consumed will not be the product of the voltsand amperes, as is the case on continuous-current circuits; but thisproduct will represent more energy than is actually consumed, owing tothe fact that the electromotive force and current-waves do not attain amaximum value at the same time, owing to what is known as a lag of thecurrent-wave behind the electromotive-force wave. When the current-waveis in unison with the impressed electromotive-force wave, or, in otherwords, when the circuit is resonant, the energy consumed is the greatestpossible for this current and electromotive force. Vhen the current lagsninety degrees behind the impressed electromotive force, the energyconsumed is zero. Now in a meter of the class referred to a maximumregistration for a given current and electrometive force is effectedwhen the magnetism of one set of field-coils is in exact phase with themain working current and the magnetism of the other coils lags exactlyninety degrees behind the working current, or, in other words,\vl1eneverthere is ninety degrees difference in phase between the magnetic fluxesinduced, respectively, by the current and potential coils of the meter.A minimum or zero registration would be effectedthat is, the meter wouldnot register at all--if the main working current should lag ninetydegrees, for then the two meterfields will be coincident in phase andwill not produce rotation. From this it will be seenthat forcorrectregistration of the energy of currents of various degrees of lagthe dierence of phase of the two magnetic fields of the meter should bethe complement of the angle of lag of the working current. This resultalways obtains if current and potential magnetic fluxes, due to theseries and shunt-field coils of the meter, have a normal phasedifference of ninety degrees when the circuit is resonant, with thecurrent invphase with the electromotive force, or whenever equivalentinductive effects are maintained acting upon the rotating member of themeter. Then starting with a resonant condition and maximum torque thephase diderence between the inducing magnetic fields will decrease whenthe current in the consumption-circuit lags, thereby decreasing thetorque of the motor mechanism in the exact ratio necessary to preserve,under varyingangles of lag, a proper registration of the trueconsumption of energy. The changes in the inductive eects of theinducing-fields upon the armature of the meter occasioned by current lagthus compensate for the correspondingly-changing ratio between the trueconsumption of energy ICO and the so-called apparent energy and renderthe meter accurate. The torque of the motor mechanism is alwaysapproximately proportional to the product of the current, electromotiveforce, and sine of the angle of current lag, and the sum of the angle ofcurrent lag in the consumption-circuit and the phase angle between theinducing-current and potential magnetic fields is equal or substantiallyequal to ninety degrees irrespective of changes in the relative valuesof these two angles.

Heretofore wattmeters have been proposed comprising a current-coil and apotential coil in which the current is lagged; but the present meterdiffers radically in having the capability for accurateself-compensation for changes in current lag above pointed out.

Figure I is a front view of a meter embodying my invention, theright-hand half thereof being shown as sectional through the center ofthe shaft to more clearly show the internal construction. Fig. 2 is aside view of the meter, partly sectioned,as described. Fig.

3 is a sectional and diagrammatic view of the main portion of the meterin plan view, and Fig. 4 is a diagram showing phase relations.

The structural features of the meter herein shown are arranged in amanner similar to that set forth in United States Patent No. 494,657,granted to me April 4, 1893, to which reference may be had, like partsbeing correspondingly lettered herein, though the present meter from anelectric standpoint,

and especially in those features whereby it can meter accuratelyinductive loads, is entirelydifferent from that of the former patent.

Referring to Figs. 1, 2, and 3, S and S' are the series or currentcoils, which carry the current to be measured, said coils consisting ofa comparatively few turns of heavy wire Yor a copper ribbon wound uponsuitable spools U U of insulating material, the coils being connectedtogether in series, the other ends being connected by wires O and O tobinding-posts M and M, respectively. The shunt and potential coils T andT are arranged With their axis perpendicular to the axis of the seriescoils, so that there will be no induction between the series coils andthe shunt-coils. The shunt-coils are wound with small wire upon suitableinsulating-spools V V', these spools and the spools U U being suitablysecured to the standards C O, which latter are shown as connected at thetop by a cross-head D, carrying a suitable countingtrain K'and anadjustable bearing R. The shaft E is supported at its upper end in saidbearing and at its lower end in a step-bearing J, the shaft havingsecured thereto the armature A, mounted to revolve freely inside thefield-coils SVS' T T. As in said patent above referred to, the armatureconsists of a closed metallic circuit of such shape as to embrace asmany as possible of the magnetic lines produced by the iield-coils.

In general the construction of the armature may be varied to meetvarious conditions of practice. A variety of forms in which suchclosed-circuit armatures may be made are now well known in the art.

I have herein shown the armature as a holvlow cylinder of copper orother good conducting material, and the cylindrical part may becontinuous or it may be laminated by longitudinal cuts. Near its lowerend the shaft E carries a disk G, of copper or other conductingmaterial, revolving between the poles of the permanent magnet I in orderthat the armature be acted upon by a retarding force directlyproportional to the speed. The strength of the magnet should besufficient to render the speed slow relatively to that of synchronismand also slow enough to render the air-resistance inappreciable. Aninductance-coil is interposed in the shunt-circuit, as best shown inFig. 3, comprising an ironwire core F8, surrounded by the primary andsecondary coils Gr8 and HS, respectively. The primary coil is connectedby wires 8 4 in shunt across the mains, with the coil T in series withit, the other end of said coil being connected by wire 5 to binding-postM or to the main circuit, as clearly shown in Fig. 3. The secondary coilH8 is connected in series with the shunt-coil T by Wires S 9 and with aresistance RX, which latter may conveniently be simply a portion of thecoil T, wound with German-silver wire. The operation of this arrangementis as follows: So far as the coil T is concerned the primary coil Grsacts simply as a choking-coil to retard the phase of IOO the current inthe circuit, and, referring to I Fig. 4, if the phase of the maincurrent passing through the series coils S S is represented by line t,then the current through Gr8 and T will lag behind t something less thanninety degrees, owing to self-induction of G8 and the coil T', and thislagging current may be represented by Z. The mutual induction of coils Tand T is small as compared with that of the coils G8 and H8, inasmuch asthe latter have an iron core, while the coils T and T do not. Thecurrent in the coil T, passing through the secondary coil H8 of theinductance-coil or transformer, will therefore lag behind the current inthe coil T something less than one hundred and eighty degrees and may berepresented diagrammatically in Fig. 4 by fm. Now completing theparallelogram of forces the resultant of Z and m may be represented byr, which is shown at right angles to the line t. Changing the resistanceR has the effect of changing the length of m, Fig. 4, and also its angleto a slight extent, and it will be at once apparent thatthis provides aready method of adjusting the resultant fr to exactly a right angle orninety degrees with t. In this consideration it is of course supposedthat t is to be from a current having no lag. The magnetism of theseries .coil will be in phase with t, as the diagram explains the actionof the meter, While the magnetomotive forces IIO IIS

due to the currents in the coils T and T', though themselves dephased bya wide angle, combine to establish a second magnetic ilux proportionalto the potential of the circuit, which will be in phase with i" and ofcourse ninety degrees behind the current flux t. In this way I secure atorque in the motor mechanism of the meter which is for a given currentand electromotive force a maximum When the current is in phase with theelectromotive force in the consumption-circuit and which will decreasewhen ythe current lags in a ratio corresponding to thatin which the realenergy consumed under such conditions decreases as compared with theapparent energy or product of the volts and amperes. A motor mechanismof this character iu which the torque varies automatically in keepingwith the phase relation between the current and electromotive force inthe external circuit, as explained, in combination with the magneticdamping mechanism or any damping mechanism acting in accordance with thesame law and the recording mechanism, constitutes the essential featuresof my new meter. In so far as the electrical actions are concerned bywhich torque is established by the inductive action of the out-0fphasemagnetic fields upon the rotating member of the meter these are similarto the actions involved in the operation of the meter of my formerpatent. They are novT well understood and further explanation isunnecessary. Owing to the retarding effect of the disk G and magnet,which is proportional to the speed of revolution, the speed of the motoris kept exactly proportional to the energy consumption, and thecounting-train recording the revolutions of the armature thus affords ameasure of the energy which is being consumed in the work-circuit.

It will be noted that the inductance coil or transformer shown in thedrawings is provided with a core F8, consisting of a bundle of ironwire, and that the magnetic circuit of this core outside of the coils iscompleted through the air. The result of this open magnetic circuit isthat its permeability, taken as a whole, is practically constant andthat therefore the magnetism of the core is approximately proportionalto the magnetizingcurrent throughout a wide range. The current liowingthrough the primary circuit of this inductance-coilwill therefore varyiu direct proportion to the impressed electromotive force and in inverseproportion to the periodicity, providing that the magnetism of the coreis not allowed at any time to approach very near to saturation.

I do not limit myself to the particular form of apparatus herein shownand described,

since the form of any or all of the necessary elements may be variedgreatly without departing from the principle of action described, theprincipal features of the invention consisting not so much in the formof the elements used as in their interrelations, and all details ofconstruction may be greatly changed from those shown and describedwithout departing from the spirit of the invention.

I have shown a Working meter embodying my improvements in the formhereinset forth, because this is the form of meter in which I have heretoforeembodied and tested the invention in practice.

Having now fully described my invention, what I claim as new, and desireto secure by Letters Patent of the United States, is-

l. The combination in an electric Wattmeter of a series coil, apotential coil in a circuit of high inductance for lagging the currenttherein, an auxiliary circuit or device whose function is to stillfurther increase the phase difference between the current and potentialmagnetic fluxes up to a normal amount of ninety degrees, when thecurrent does not lag in the consumption-circuit, means for supplyingsaid auxiliary circuit or device with current independently of saidpotential coil, means for adjusting the current in said anxiliarycircuit or device, a closed-circuit armature, a magnetic dampingmechanism and a recording mechanism.

2. The combination with a ield-coil, of a second field-coil having acircuit of high selfinduction, a third held-coil deriving its currentindependently of the second ield-coil, and a closed-circuit armature ininductive relation to the coils.

3. In an electric measuringinstrument, an armature, a field-coil in acircuit of high selfinduction, a second field-coil deriving its currentinductively from the circuit of the first field-coil and independentlyof said first fieldcoil, and a third field-coil having its magnetic.axis displaced with reference to the axes of the other coils. A

4. In an electric measuring device the combination of an armature, aseries-connected field-coil, a shunt-connected iield-coil, aninductance-coil in series with the said shuntconnected field-coil, andan auxiliary coilderiving its current from a secondary winding on saidinductance-coil.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

MILTON E. THOMPSON.

Witnesses:

JOHN @.EDWARDS, HERBERT C. WIRT.

IIO

